1. Field of The Invention
The invention relates to thermoplastic molding compositions and more particularly to molding compositions which are blends of polyester-carbonate and polyetherimide resins.
2. Brief Description of the Related Art
Polyester-carbonates (also known as copolyester-polycarbonates) are a well known class of thermoplastic resin as is their preparation; see for example the descriptions given in U.S. Pat. Nos. 3,169,121 and 4,487,896.
Polyester-carbonate (PPC) resins have been useful as ingredients in blends of thermoplastic molding resins, to mold particular articles of certain physical properties. For example, U.S. Pat. No. 4,430,484 (Quinn) issued Feb. 7, 1984, describes blends of polyester-carbonates with polyetherimides as useful to mold articles showing improved, higher heat distortion temperature under load. However, articles molded from the exemplified blends exhibit some brittleness when subjected to testing for notched Izod impact strengths.
In copending U.S. patent application Ser. No. 716,940 assigned to the assignee of interest of the present application and filed Jun. 18, 1991 abandoned, ternary blends of polyetherimides, siloxane polyetherimide copolymers and polycarbonate resins including polyester-carbonate resins are described broadly as thermoplastically moldable to obtain ductile articles with improved flame retardance and strength properties useful in engineering thermoplastics. The disclosure however does not include actual examples of specific blend formulations containing polyester-carbonate resins, with characterization of the associated physical properties. In fact, many (but not all) blends of polyester-carbonate resins with polyetherimides and siloxane polyetherimide copolymers yield brittle (non-ductile) articles when thermoplastically molded. We have studied this puzzling situation and discovered that the ductility of polyester-carbonate resin-polyetherimide or polyarylate-polyetherimide resin blend generated articles is dependent on a plurality of factors not previously appreciated.
First, we have discovered that the average ester content of the total blend composition is critical to the achievement of ductility in articles molded from polyester-carbonate resins or polyarylate resins blended with polyetherimide, alone or with siloxane-polyetherimides.
Second, we have discovered that articles thermoplastically molded from blends of polyester-carbonate and polyetherimide resins with or without the presence of a siloxane-polyetherimide copolymer can exhibit both ductility and high heat distortion temperature under load, when the polyester-carbonate resin ingredient is selected from a particular class of resins, characterized by a particular chain structure. The improved articles (in respect to ductility) are useful for example, as interior body components of automobiles, aircraft and like vehicles. The high heat distortion under load values are particularly useful in the thermoforming of laminate panels.